The alpha/beta hydrolase fold is one of the most versatile structures in the protein realm according to the diversity of sequences adopting such a three dimensional architecture. We found that the versatility of a canonical alpha/beta-hydrolase fold, particularly that of the carboxylesterase Cest-2923 from the lactic acid bacterium Lactobacillus plantarum WCFS1, also extends to its oligomeric behavior in solution. Thus, we discovered that Cest-2923 exhibits a pH-dependent pleomorphic behaviour in solution involving monomers, canonical dimers and tetramers. Whereas at neutral pH the system is mainly shifted to dimeric species, at acidic conditions tetrameric species predominate. Interestingly, despite that these tetramers result from the association of canonical dimers, as commonly found in many other carboxylesterases from the hormone-sensitive lipase family, they can be defined as “non canonical” since they represent a different association mode. The observed associative behaviour is consistent with different crystallographic results of Cest-2923 from structural genomics consortia. Finally, we benefit from the presence of sulphate or acetate molecules (depending on the crystal form analysed) in the close vicinity of the nucleophile Ser116, to identify interactions with the putative oxyanion hole and also to deduce the existence of hydrolytic activity within Cest-2923 crystals.

Reference:
Benavente R, Esteban-Torres M, Acebrón I, de Las Rivas B, Muñoz R, Alvarez Y, Mancheño JM. “Structure, biochemical characterization and analysis of the pleomorphism of carboxylesterase Cest-2923 from Lactobacillus plantarum WCFS1”. FEBS J. 2013 Oct 16. doi: 10.1111/febs.12569.